A wind turbine power train has to transmit an input torque at a speed from a low speed shaft (associated with rotor and blades) to a high speed shaft (associated with a generator that converts said input torque at a given speed into electric power).
Current wind turbines are fatigue critical machines so it is important to know the value of said input torque at the low speed shaft of the wind turbine power train in order to estimate the fatigue damage for the design of the power train and/or maintenance operations in each wind turbine. This can be carried out by determining the torque oscillations in the power train, particularly in the low speed shaft.
Conventionally, an operating control and data log system may provide accurate values concerning electric power in the generator and angular velocity in the generator (i.e. the high speed shaft). However, input torque values in the rotor (low speed shaft) and angular velocity values in said low speed shaft are difficult to be accurately obtained. Due to this lack of input torque values at the low speed shaft, it is not possible at present to directly and readily obtain the values for the torque to which the wind turbine power train is subjected.
Low speed shaft torque values are typically obtained by experimental methods in combination with mechanical measurements through strain gauge means by directly measuring stress values at the low speed shaft. This is capital intensive, specially taking into consideration the fact that this has to be done for each power train.